Colour laser marking methods of security documents

ABSTRACT

A security document precursor including, in order: a) at least one transparent biaxially stretched polyester foil; b) one colourless colour forming layer containing at least an infrared absorber, a colourless dye-precursor and a polymeric binder; and c) a polymeric support; wherein the polymeric binder is copolymer including at least 90 wt % of a chlorinated ethylene and 1 wt % to 10 wt % of vinyl acetate both based on the total weight of the binder. Methods for making the security document precursor are also disclosed.

TECHNICAL FIELD

This invention relates to methods for colour laser marking securitydocument precursors and to the resulting laser marked securitydocuments.

BACKGROUND ART

Security cards are widely used for various applications such asidentification purposes (ID cards) and financial transfers (creditcards). Such cards typically consist of a laminated structure consistingof various paper or plastic laminates and layers wherein some of themmay carry alphanumeric data and a picture of the card holder. So called‘smart cards’ can also store digital information by including anelectronic chip in the card body.

A principal objective of such security cards is that they cannot beeasily modified or reproduced in such a way that the modification orreproduction is difficult to distinguish from the original.

Two techniques frequently used for preparing security documents arelaser marking and laser engraving. In literature, laser engraving isoften incorrectly used for laser marking. In laser marking, a colourchange is observed by local heating of material, while in laserengraving material is removed by laser ablation.

US 2005001419 (DIGIMARK) discloses a colour laser engraving method and asecurity document including an opaque surface layer and one or morecoloured sub-layers. A laser provides openings in the surface layer toexpose the colour of the sub-layer thereby creating colour images andtext.

WO 2009/140083 (3M) discloses methods to generate a colour image in amultilayer article containing at least one thermally activatable layercoated from a composition including a non-linear light to heatconverter, a leuco dye, a thermal acid generator and a solvent. A colourimage is formed in the colour forming layer upon activation withnon-linear light beam radiation (300-1500 nm).

U.S. Pat. No. 7,158,145 (ORGA SYSTEMS) discloses a three-wavelengthsystem (440, 532 and 660 nm) for applying coloured information to adocument by means of wavelength-selective bleaching of chromophoricparticles in a layer close to the surface.

U.S. Pat. No. 4,720,449 (POLAROID) discloses a thermal imaging methodfor producing colour images on a support carrying at least one layer ofa colourless compound, such as di- or triarylmethane, by directapplication of heat or by conversion of electromagnetic radiation intoheat. The laser beam may have different wavelengths, typically in arange above 700 nm with at least about 60 nm apart so that each imaginglayer may be exposed separately to convert a colourless triarylmethanecompound into a coloured form, such as yellow, magenta, cyan or black,by controlling the focusing depth of the laser beam source to eachcolour forming layer. The colour forming compositions include di- ortriarylmethane compounds, infrared absorbers, acidic substances andbinders.

U.S. Pat. No. 4,663,518 (POLAROID) discloses a laser printing method foractivating heat sensitive image forming dyes in three different layerson a support to card holder, coloured text and machine readable digitalcode.

Suitable binders that may be used in U.S. Pat. No. 4,720,449 (POLAROID)and U.S. Pat. No. 4,663,518 (POLAROID) include polyvinyl alcohol,polyvinyl pyrrolidone, methyl cellulose, cellulose acetate butyrate,copolymers of styrene and butadiene, polymethyl methacrylate, copolymersof methyl and ethyl acrylate, polyvinyl acetate, polyvinyl chloride andpolyvinyl butyral. These binders are commonly employed in heat sensitiverecording elements because of their inertness, i.e. they do not have anyadverse effect on the colour formation reaction. However, adhesionproblems have frequently been observed with these binders. Adhesion isan important aspect for security documents since poor adhesion allowsdelamination and thus falsification of the laser marked image inside thesecurity document.

Therefore, it would be desirable to have a secure colour laser markingsystem for producing security documents which combines good adhesion andgood image quality.

SUMMARY OF INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a security document precursor asdefined by claim 1.

It is a further object of the present invention to provide a method formanufacturing the security document precursors having a good imagequality and which are more difficult to falsify.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

Definitions

The term “graphical data” as used in disclosing the present inventionmeans any graphical representation, e.g. a picture of a person, adrawing, etc.

The term “information” as used in disclosing the present invention meansany alphanumeric data, e.g. name, place of birth, date of birth, etc.

The term “image” as used in disclosing the present invention means anygraphical data and information. The image on a security documentpreferably varies at least partially from one security document toanother one.

The term “security document” as used in disclosing the present inventionmeans a document which contains the required image, e.g. a validpassport or identification card, and is ready for use.

The term “security document precursor” as used in disclosing the presentinvention means a document not containing all the required components ofthe security document, e.g. a layer or a security feature, and/or notcontaining the required image of the security document.

The term “visible spectrum” as used in disclosing the present inventionmeans the electromagnetic spectrum from 400 nm to 700 nm.

The term “polymeric foil” as used in disclosing the present invention,means a self-supporting polymer-based sheet, which may be associatedwith one or more adhesion layers e.g. subbing layers. Foils aregenerally manufactured through extrusion.

The term “support” as used in disclosing the present invention, means aself-supporting polymer-based sheet, which may be transparent but ispreferably opaque and which may be associated with one or more adhesionlayers e.g. subbing layers. Supports are generally manufactured throughextrusion.

The term “layer”, as used in disclosing the present invention, isconsidered not to be self-supporting and is manufactured by coating iton a support or a polymeric foil.

“PET” is an abbreviation for polyethylene terephthalate.

“PETG” is an abbreviation for polyethylene terephthalate glycol, theglycol indicating glycol modifiers which are incorporated to minimizebrittleness and premature aging that occur if unmodified amorphouspolyethylene terephthalate (APET) is used in the production of cards.

“PET-C” is an abbreviation for crystalline PET, i.e. a biaxiallystretched polyethylene terephthalate. Such a polyethylene terephthalatesupport or foil has excellent properties of dimensional stability.

The definitions of security features correspond with the normaldefinition as adhered to in the “Glossary of Security Documents-Securityfeatures and other related technical terms” as published by theConsilium of the Council of the European Union on August 25, 2008(Version: v.10329.02.b.en) on its website:http://www.consilium.europa.eu/prado/EN/glossaryPopup.html.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The term “substituted” in, for example substituted alkyl, means that thesubstituent on alkyl contains at least one atom different from carbon orhydrogen. The substituent may be a single atom (e.g. a halogen) or agroup of atoms containing at least one atom different from carbon orhydrogen (e.g. an acrylate group).

The term “chlorinated ethylene”, as used in disclosing the presentinvention, means ethylene substituted with at least one chlorine atome.g. vinyl chloride, vinylidene chloride, 1,2-dichloro-ethylene,trichloroethylene and tetrachloroethylene. Trichloroethylene andtetrachloroethylene are all much more difficult to polymerize than vinylchloride or vinylidene chloride.

A leuco dye is a well-known colour forming compound whose molecules canacquire two forms, one of which is colourless. An example of a leuco dyeis crystal violet lactone, which in its lactone form is colourless, butwhen it is protonated becomes intensely violet.

Security Documents and Precursors

The security document precursor according to the present invention hasat least one colourless colour forming layer including at least:

-   -   a) an infrared absorber;    -   b) a colourless dye-precursor; and    -   c) a polymeric binder;    -   wherein the polymeric binder is a copolymer including at least        90 wt % of a chlorinated ethylene and 1 wt % to 10 wt % of vinyl        acetate both based on the total weight of the binder.

The security document precursor may further include d) a thermal acidgenerating compound.

The colourless colour forming layer(s) can be coated onto the polyesterfoil by any conventional coating technique, such as dip coating, knifecoating, extrusion coating, spin coating, slide hopper coating andcurtain coating. Preferably the colourless colour forming layer iscoated with a slide hopper coater or a curtain coater, more preferablycoated onto the transparent polymeric foil including a subbing layer.

The dry thickness of the colourless colour forming layer is preferablybetween 5 and 40 g/m², more preferably between 7 and 25 g/m², and mostpreferably between 10 and 15 g/m².

The security document precursor according to present invention containsat least one colourless colour forming layer, but preferably containstwo, three or more colourless colour forming layers containing differentinfrared absorbers and colour forming compounds for producing amulti-coloured security document.

The infrared absorber not only delivers the heat for the colour formingaction, but also has the advantage that there is no or minimalabsorption in the visible spectrum and thus also no or minimalinterference with the colours formed by the one or more colourlesscolour forming layers. This also allows having, for example, a purewhite background in a security document.

The security document precursor preferably contains colourless colourforming layers for forming a cyan, a magenta and a yellow image or forforming a red, a blue and a green image, since most colour managementsystems for producing colour images are based on either a CMY or RGBcolour reproduction.

Colour Laser Marking

The security document precursor is laser marked using one or moreinfrared lasers. The colourless colour forming layer includes aninfrared absorber which is capable of converting the infrared radiationof the infrared laser into heat which triggers the colour formationreaction. Hence, the laser emission wavelength of the infrared laserpreferably matches the absorption maximum of the infrared dye within 40nm, more preferably within 25 nm.

The infrared laser used in the method of colour laser marking a securitydocument precursor is preferably an optically pumped semiconductor laseror a solid state Q-switched laser.

A semiconductor laser is particularly preferred because the device iscompact and inexpensive. Most semiconductor lasers are laser diodes,which are pumped with an electrical current in a region where n-dopedand p-doped semiconductor material meet. However, there are alsooptically pumped semiconductor lasers, where carriers are generated byabsorbed pump light. Optically pumped semiconductor lasers have theadvantage of unique wavelength flexibility, different from any othersolid-state based laser. The fundamental near-IR output wavelength isdetermined by the structure of the gain chip (e.g. the semiconductorInGaAs), and can be set anywhere between about 920 nm and about 1150 nm.This allows a perfect match between the laser emission wavelength andthe infrared dye absorption maximum.

The infrared laser is most preferably a solid state Q-switched laser.Q-switching is a technique by which a laser can be made to produce apulsed output beam. The technique allows the production of light pulseswith extremely high peak power, much higher than would be produced bythe same laser if it were operating in a continuous wave (constantoutput) mode, Q-switching leads to much lower pulse repetition rates,much higher pulse energies, and much longer pulse durations.

Infrared lasers are widely commercially available. An example of a solidstate Q-switched laser is the Matrix™ 1064 laser from COHERENT emittingat 1064 nm and capable of producing an average power of 7 Watt at apulse repetition rate of 10 kHz.

Colourless Dye-Precursors

Colourless dye-precursors are colourless or slightly yellowish compoundswhich react into a coloured form.

The colourless dye-precursor is preferably present in the colourlesscolour forming layer in an amount of 0.5 to 5.0 g/m², more preferably inan amount of 1.0 to 3.0 g/m².

For performing the method of colour laser marking according to thepresent invention, the following reaction mechanisms and colour formingcompounds involved are suitable to form a coloured dye.

1. Fragmentation of a Colourless Dye-Precursor

The reaction mechanism can be represented by:

-   -   Colourless dye-FG→Dye        wherein FG represents a fragmenting group.

Such a reaction mechanism is explained in more detail by U.S. Pat. No.5,243,052 (POLAROID) disclosing the colour formation by fragmentation ofa mixed carbonate ester of a quinophthalone dye and a tertiary alkanolcontaining not more than about 9 carbon atoms.

The fragmentation of a colourless dye-precursor may be catalyzed oramplified by acid generating agents. The dyes G-(18) to G-(36) disclosedby U.S. Pat. No. 6,100,009 (FUJI) are catalyzed or amplified bypolymeric acid generating agents based on A-(1) to A-(52), which arealso suitable as acid generating agents in the present invention.

Another preferred colourless dye-precursor is the leuco dye-precursor(CASRN104434-37-9) shown in EP 174054 A (POLAROID) which discloses athermal imaging method for forming colour images by the irreversibleunimolecular fragmentation of one or more thermally unstable carbamatemoieties of an organic compound to give a visually discernible colourshift from colourless to coloured.

The fragmentation of a leuco dye-precursor may be a two-step reactionmechanism represented by:

-   -   Leuco-dye-FG→[Leuco-dye]→Coloured Dye        wherein FG represents a fragmenting group.

The fragmentation of the colourless leuco dye-precursor may be catalyzedor amplified by acids and acid generating agents. The leucodye-precursors G-(1) to G-(17) disclosed by U.S. Pat. No. 6,100,009(FUJI) are catalyzed or amplified by polymeric acid generating agentsbased on A-(1) to A-(52), which are also suitable as acid generatingagents in the present invention.

2. Protonation of a Leuco Dye after Fragmentation of a H-Donor-Precursor

The reaction mechanism can be represented by:

-   -   Leuco-dye+H-donor-FG→Leuco-dye+H-donor→Coloured Dye        wherein FG represents a fragmenting group.

A preferred H-donor-FG compound includes an ester group as part of itschemical structure (the rest of the compound is represented by the groupT) which by laser heating forms a carboxylic acid group:

A more preferred H-donor-precursor includes a carbonate group, e.g. atBOC group, as part of its chemical structure (the rest of the compoundis represented by the group T) which by laser heating forms a phenolgroup:

Preferred carbonate groups are given on page 8 of EP 605149 A (JUJOPAPER). In a preferred embodiment, the H-donor-FG compound contains 2carbonate groups.

The most preferred H-donor-FG compound is:

The synthesis of compound HDP (CASRN 129104-70-7) is given on page 31 ofEP 605149 A (JUJO PAPER) for the compound (19).

In addition to the H-donor, the fragmentation of the H-donor-FG compoundabove also leads to the formation of a compound having a meltingtemperature lower than room temperature (20° C.). In the presentinvention the formation of such a compound is used as an additionalsecurity feature. After producing a security document by the method ofcolour laser marking according to the present invention wherein abiaxially stretched polyester foil is used as overlay, the compoundhaving a melting temperature lower than room temperature will disturb asecond laser marking (falsification of the security document) by theformation of visible blisters in laser marked areas.

3. Protonation of a Leuco Dye after a Re-Arrangement in aH-Donor-Precursor

The reaction mechanism can be represented by:

-   -   Leuco-dye+H-donor-RG→Leuco-dye+H-donor→Coloured Dye        wherein RG represents a rearranging group.

A preferred H-donor-RG compound is capable of forming a compound havingan allyl substituted phenol group as part of its chemical structure (therest of the compound is represented by the group T) by laser heating:

Preferred H-donor-RG compounds include 4-hydroxy-4′-allyloxydiphenylsulfone and 4,4′-diallyloxy diphenylsulfone whereof thesynthesis is disclosed by EP 1452334 A (RICOH).

In contrast to the H-donor-FG compound of reaction mechanism 2, nocompound having a melting temperature lower than room temperature (20°C.) is produced by the rearrangement of the H-donor-precursor to ahydrogen donor. Consequently, the security feature of blister formationas possible with the H-donor-FG compound cannot be produced by theH-donor-RG compounds.

The colour formation according to the mechanisms 2 and 3 above aretwo-component reactions involving a colourless leuco dye and a hydrogendonor-precursor, i.e. a ‘H-donor-FG compound’ or ‘H-donor-RG compound’,while the first reaction mechanism is an one-component reactions. Theadvantage of using a two-component reaction for the colour formation isthat the stability, especially the shelf-life stability, can beenhanced. The probability of undesired colour formation due toenvironment heating is decreased by going from a single step reaction toa two step reaction involving the formation of the H-donor followed by areaction of the formed H-donor with the leuco dye.

The preferred colour formation mechanism is the protonation of a leucodye after fragmentation of the H-donor-precursor since it includes bothadvantages of the blister formation security feature and the enhancedshelf-life stability.

In a preferred embodiment of the colourless colour forming layer, acombination is used of 4,4′-Bis(tert-butoxycarbonyloxy)diphenylsulfone(CASRN 129104-70-7) as the H-donor-FG compound with the colourless leucodye crystal violet lactone (CASRN 1552-42-7).

Infrared Absorbers

The infrared absorber used in the colourless colour forming layer of thesecurity document precursor according to the present invention, can bean infrared dye, an infrared organic pigment and an inorganic infraredpigment, but preferably the infrared absorber is an infrared dye.

The advantage of using infrared dyes is that the absorption spectrum ofan infrared dye tends to be narrower than that of an infrared pigment.This allows the production of multicoloured articles and securitydocuments from precursors having a plurality of colourless colourforming layers containing different infrared dyes and colour formingcompounds. The infrared dyes having a different λ_(max) can then beaddressed by infrared lasers with corresponding emission wavelengthscausing colour formation only in the colourless colour forming layer ofthe addressed infrared dye.

Suitable examples of infrared dyes include, but are not limited to,polymethyl indoliums, metal complex IR dyes, indocyanine green,polymethine dyes, croconium dyes, cyanine dyes, merocyanine dyes,squarylium dyes, chalcogenopyryloarylidene dyes, metal thiolate complexdyes, bis(chalcogenopyrylo)polymethine dyes, oxyindolizine dyes,bis(aminoaryl)polymethine dyes, indolizine dyes, pyrylium dyes, quinoiddyes, quinone dyes, phthalocyanine dyes, naphthalocyanine dyes, azodyes, (metalized) azomethine dyes and combinations thereof.

Suitable inorganic infrared pigments include ferric oxide, carbon blackand the like.

A preferred infrared dye is5-[2,5-bis[2-[1-(1-methylbutyl)benz[cd]indol-2(1H)-ylidene]ethylidene]cyclopentylidene]-1-butyl-3-(2-methoxy-1-methylethyl)-2,4,6(1H,3H,5H)-pyrimidinetrione(CASRN 223717-84-8) represented by the Formula IR-1:

The infrared dye IR-1 has an absorption maximum λ_(max) of 1052 nmmaking it very suitable for a Nd-YAG laser having an emission wavelengthof 1064 nm.

The infrared red absorber is preferably present in the colourless colourforming layer in an amount of 0.05 to 1.0 g/m², more preferably in anamount of 0.1 to 0.5 g/m².

Thermal Acid Generating Compounds

The fragmentation of a colourless dye-precursor in the colourless colourforming layer of the security document precursor may be catalyzed oramplified by acids and acid generating agents.

Suitable thermal acid generating agents may be the polymeric acidgenerating agents based the ethylenically unsaturated polymerizablecompounds A-(1) to A-(52) disclosed by U.S. Pat. No. 6,100,009 (FUJI)and herein incorporated as a specific reference.

Suitable non-polymeric acid generating agents are the compounds A-(1) toA-(52) disclosed by U.S. Pat. No. 6,100,009 (FUJI) lacking theethylenically unsaturated polymerizable group.

The thermal acid generating agent is preferably present in the amount of10 to 20 wt %, more preferably 14 to 16 wt % based on the total dryweight of the colourless colour forming layer.

Polymeric Binders

The polymeric binder of the at least one colourless colour forming layerin the security document precursor according to the present invention isa copolymer including at least 90 wt % of a chlorinated ethylene and 1wt % to 10 wt % of vinyl acetate both based on the total weight of thebinder.

In a preferred embodiment, the polymeric binder includes vinyl chlorideas the chlorinated ethylene.

In a more preferred embodiment, the chlorinated ethylene in thepolymeric binder consists of vinyl chloride.

The polymeric binder of the security document precursor according to thepresent invention preferably includes at least 90 wt % of vinylchloride, more preferably at least 93 wt % of vinyl chloride.

The polymeric binder of the security document precursor according to thepresent invention preferably includes at least 4 wt % of vinyl acetate,more preferably at least 90 wt % of vinyl chloride and at least 4 wt %of vinyl acetate, because this results in lower minimum opticaldensities.

In a preferred embodiment, the polymeric binder consists of at least 90wt % of a chlorinated ethylene and 1 wt % to 10 wt %, preferably 4 wt %to 8 wt % of vinyl acetate both based on the total weight of the binder.

The polymeric binder is preferably present in the colourless colourforming layer in an amount of 5 to 30 g/m², more preferably in an amountof 7 to 20 g/m².

In the most preferred embodiment, the colourless colour forming layer inthe method of colour laser marking an security document precursoraccording to the present invention includes4,4′-Bis(tert-butoxycarbonyloxy)diphenylsulfone as hydrogendonor-precursor and crystal violet lactone as the colour formingcolourless dye-precursor and a copolymer including at least 90 wt % of avinyl chloride and 1 wt % to 10 wt % of vinyl acetate both based on thetotal weight of the binder.

Transparent Biaxially Stretched Polyester Foils

In the present invention, the colourless colour forming layer containingan infrared absorber, a polymeric binder and a colour forming compoundis coated on a biaxially stretched polyester foil, preferably on abiaxially stretched polyethylene terephthalate foil, both optionallyprovided with a subbing layer.

The transparency of the biaxially stretched polyester foil is requiredso that the infrared laser light can reach the colourless colour forminglayer and that information and graphical data, e.g. security print andguilloches, can be observed in and underneath the laser markedcolourless colour forming layer(s).

An advantage of using a biaxially stretched polyethylene terephthalatefoil as the transparent polyester foil is that is very durable andresistant to mechanical influences (flexion, torsion, scratches),chemical substances, moisture and temperature ranges. This is especiallyuseful for security documents such as identification cards and creditcards for which the average daily usage has lately augmentedsubstantially from less than 1 time per week to 4 times per day. Thecard body has to withstand not only this increased usage, but also theassociated storage conditions. Cards are no longer safely tucked away incabinets at home or seldom-opened wallets, but are now loosely put awayin pockets, purses, sport bags etc.—ready for immediate use. PVC(polyvinylchloride) is the most widely used material for plastic cardsbut has low durability of the card body, resulting in an effectivelifetime of only 1-3 years, much lower than the lifetime of the oftenexpensive chips included in the card. Other materials like Teslin™ andABS are only suitable for very low-end or single-use cards. PC(polycarbonate) can be used for longer-life and more secure ID cards,but has a high production cost and a low resistance to torsion,scratching and chemicals.

The biaxially stretched polyester foil (e.g. PET-C foil) should besufficiently thick to be self-supporting, but thin enough so that it ispossible to include other layers, foils and support within the format asspecified for security documents, e.g. by ISO 7810 for identity cards.The thickness of the PET-C foil is preferably between 10 μm and 200 μm,more preferably between 10 μm and 100 μm, most preferably 30 μm and 65μm.

The transparent biaxially stretched polyester foil (e.g. PET-C foil)with the at least one colourless colour forming layer may be laminatedonto a polymeric support, e.g. a lasermarkable polymeric support or asupport coated with a lasermarkable layer for generating a black colour,forming a security document wherein the colourless colour forming layeris sandwiched between the transparent biaxially stretched polyester foiland the support. Additional foils and layers, e.g. other colourlesscolour forming layers having different infrared absorbers and colourforming compounds, may be included between the polymeric support and thetransparent biaxially stretched polyester foil. In the case of a fullycoloured security document, at least three colourless colour forminglayers are present between the transparent biaxially stretched polyesterfoil and the support for forming e.g. the CMYK colours.

In a preferred embodiment, the security document is symmetrical, i.e.the same layers and foils are present on both sides of the support. Thishas the advantages that both sides can be colour laser marked and thatpossible curl due to an asymmetric construction of the security documentis effectively prevented.

In order to comply with the format as specified by ISO 7810 for securitydocuments, the transparent biaxially stretched polyester or PET-C foiland the support have a thickness of between about 6 μm and about 250 μm,more preferably between about 10 μm and about 150 μm, most preferablybetween about 20 μm and about 100 μm.

Polymeric Supports

The polymeric support can be transparent, translucent or opaque, but ispreferably an opaque support. The advantage of an opaque support,preferably of a white colour, is that any information on the securitydocument is more easily readable and that a colour image is moreappealing by having a white background.

The polymeric support is preferably a single component extrudate, butmay also be co-extrudate. Examples of suitable co-extrudates arePET/PETG and PET/PC.

Polymeric supports include cellulose acetate propionate or celluloseacetate butyrate, polyesters such as polyethylene terephthalate andpolyethylene naphthalate, polyamides, polycarbonates, polyimides,polyolefins, poly(vinylacetals), polyvinylchlorides, polyethers andpolysulphonamides.

Also synthetic paper can be used as a polymeric support, for example,Synaps™ synthetic paper of Agfa-Gevaert NV.

Other examples of useful high-quality polymeric supports for the presentinvention include opaque white polyesters and extrusion blends ofpolyethylene terephthalate and polypropylene. Also Teslin™ may be usedas support.

Polyester supports and especially polyethylene terephthalate supportsare preferred because of their excellent properties of dimensionalstability. When such a polyester is used as the support material, asubbing layer may be employed to improve the bonding of layers, foilsand/or laminates to the support.

In a preferred embodiment of the security document precursor accordingto the present invention, the support is polyvinyl chloride,polycarbonate or polyester, with coloured or whitened polyvinylchloride, polycarbonate or polyester being preferred. The polyestersupport is preferably polyethylene terephthalate support (PET) orpolyethylene terephthalate glycol (PETG).

Instead of a coloured or whitened support, an opacifying layer can becoated onto the support. Such opacifying layer preferably contains awhite pigment with a refractive index greater than 1.60, preferablygreater than 2.00, and most preferably greater than 2.60. The whitepigments may be employed singly or in combination. Suitable whitepigments include C.I. Pigment White 1, 3, 4, 5, 6, 7, 10, 11, 12, 14,17, 18, 19, 21, 24, 25, 27, 28 and 32. Preferably titanium dioxide isused as pigment with a refractive index greater than 1.60. Titaniumoxide occurs in the crystalline forms of anatase type, rutile type andbrookite type. In the present invention the rutile type is preferredbecause it has a very high refractive index, exhibiting a high coveringpower.

In one embodiment of the security document precursor according to thepresent invention, the support is an opacified polyvinyl chloride, anopacified polycarbonate or an opacified polyester.

The manufacturing of biaxially stretched polyester foils and supports iswell-known in the art of preparing suitable supports for silver halidephotographic films. For example, GB 811066 (ICI) teaches a process toproduce biaxially oriented films of polyethylene terephthalate.

The polyethylene terephthalate foils and supports are preferablybiaxially stretched with a stretching factor of at least 2.0, morepreferably at least 3.0 and most preferably a stretching factor of about3.5. The temperature used during stretching is preferably about 160° C.

Methods to obtain opaque polyethylene terephthalate substrates andbiaxially oriented films thereof of have been disclosed in, e.g. US2008238086 (AGFA).

Subbing Layers

The polyester foil and polymeric support may be provided with one ormore subbing layers. This has the advantage that the adhesion between alayer, such as the colourless colour forming layer, and the polyesterfoil or polymeric support is improved. The transparent polyester foilpreferably includes a subbing layer whereon the colourless colourforming layer is coated.

Useful subbing layers for this purpose are well known in thephotographic art and include, for example, polymers of vinylidenechloride such as vinylidene chloride/acrylonitrile/acrylic acidterpolymers or vinylidene chloride/methyl acrylate/itaconic acidterpolymers.

The application of subbing layers is well-known in the art ofmanufacturing polyester supports for silver halide photographic films.For example, the preparation of such subbing layers is disclosed in U.S.Pat. No. 3,649,336 (AGFA) and GB 1441591 (AGFA) ;

Suitable vinylidene chloride copolymers include: the copolymer ofvinylidene chloride, N-tert.-butylacrylamide, n-butyl acrylate, andN-vinyl pyrrolidone (e.g.70:23:3:4), the copolymer of vinylidenechloride, N-tert.-butylacrylamide, n-butyl acrylate, and itaconic acid(e.g. 70:21:5:2), the copolymer of vinylidene chloride,N-tert.-butylacrylamide, and itaconic acid (e.g. 88:10:2), the copolymerof vinylidene chloride, n-butylmaleimide, and itaconic acid (e.g.90:8:2), the copolymer of vinyl chloride, vinylidene chloride, andmethacrylic acid (e.g. 65:30:5), the copolymer of vinylidene chloride,vinyl chloride, and itaconic acid (e.g. 70:26:4), the copolymer of vinylchloride, n-butyl acrylate, and itaconic acid (e.g. 66:30:4), thecopolymer of vinylidene chloride, n-butyl acrylate, and itaconic acid(e.g. 80:18:2), the copolymer of vinylidene chloride, methyl acrylate,and itaconic acid (e.g.90:8:2), the copolymer of vinyl chloride,vinylidene chloride, N-tert.-butylacrylamide, and itaconic acid (e.g.50:30:18:2). All the ratios given between brackets in theabove-mentioned copolymers are ratios by weight.

In a preferred embodiment, the subbing layer has a dry thickness of nomore than 2 μm or preferably no more than 200 mg/m².

Organic Solvents

For coating the colourless colour forming layer, one or more organicsolvents may be used. The use of an organic solvent facilitates thedissolution of the polymeric binder and specific ingredients such as theinfrared dye.

A preferred organic solvent is methylethylketon (MEK) because itcombines a high solubilizing power for a wide range of ingredients andit provides, on coating the colourless colour forming layer, a goodcompromise between the fast drying of the colourless colour forminglayer(s) and the danger of fire or explosion thereby allowing highcoating speeds.

Other Security Features

To prevent forgeries of identification documents, different means ofsecuring are used. One solution consists in superimposing lines orguilloches on an identification picture such as a photograph. In thatway, if any material is printed subsequently, the guilloches appear inwhite on added black background. Other solutions consist in addingsecurity elements such as information printed with ink that reacts toultraviolet radiation, micro-letters concealed in an image or text etc.

The security document according to the present invention may containother security features such as anti-copy patterns, guilloches, endlesstext, miniprint, microprint, nanoprint, rainbow colouring, 1D-barcode,2D-barcode, coloured fibres, fluorescent fibres and planchettes,fluorescent pigments, OVD and DOVID (such as holograms, 2D and 3Dholograms, kinegrams™, overprint, relief embossing, perforations,metallic pigments, magnetic material, Metamora colours, microchips, RFIDchips, images made with OVI (Optically Variable Ink) such as iridescentand photochromic ink, images made with thermochromic ink, phosphorescentpigments and dyes, watermarks including duotone and multitonewatermarks, ghost images and security threads.

A combination of the security document according to the presentinvention with one of the above security features increases thedifficulty for falsifying the document.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS(Belgium) unless otherwise specified. The water used was deionizedwater.

CCE is Bayhydrol H 2558, a anionic polyester urethane (37.3%) fromBAYER.

Resorcinol from Sumitomo Chemicals.

Par is a dimethyltrimethylolamine formaldehyde resin from Cytecindustries.

PAR-sol is a 40 wt % aqueous solution of Par.

PEA is Tospearl 120 from Momentive Performance materials.

PEA-sol is a 10 wt % (50/50) aqueous/ethanol dispersion of PEA.

Dowfax™ 2A1 from Pilot Chemicals C is a Alkyldiphenyloxide disulfonate(4.5% wt %).

DOW-sol is a 2.5 wt % solution of Dowfax™ 2A1 in isopropanol.

Surfynol™ 420 from Air Products is a non ionic surfactant.

Surfynsol is a 2.5 wt % solution of Surfynol™ 420 in iso propanol.

MEK is an abbreviation used for methylethylketon.

UCAR is an abbreviation for a 25 wt % solution in MEK of UCARTM VAGD.

Baysilon is a 1 wt % solution in MEK of the silicon oil BaysilonTMLackadditive MA available from BAYER.

HDP is the hydrogen donor-precursor CASRN 129104-70-7 prepared accordingto the synthesis given on page 31 of EP 605149 A (JUJO PAPER) for thecompound (19).

CVL is crystal violet lactone is CASRN 1552-42-7 available fromPharmorgana:

S-Lec™ BL5 HP Z is a polyvinyl acetal polymer prepared by acetalisationof a copolymer of vinylalcohol and vinyl acetate with butryaldehyde,manufactured by Sekisui, Japan.

Elvacite™ 2010 is a polymethyl methacrylate grade available from LuciteInternational, USA.

CAB 381-2 is a cellulose acetate butyrate grade manufactured by EastmanChemical and provided by Barentz.

Vinnol™ E15/48A is a hydroxyl-containing copolymer of 84 wt % vinylchloride and 16 wt % of acrylic acid esters (2-hydroxypropyl acrylate)provided by Wacker AG.

UCAR™ VAGC is a medium molecular weight, hydroxyl-functional terpolymercomprised of 81% vinyl chloride, 4% vinyl acetate, and 15% of ahydroxyalkyl acrylate (2-hydroxypropyl acrylate) provided by DowChemical.

Vinnol™ H40/43 is a copolymer of 66 wt % vinyl chloride and 34 wt % ofvinyl acetate provided by Wacker AG.

Vinnol™ H40/60 is a copolymer of 61 wt % vinyl chloride and 39 wt % ofvinyl acetate provided by Wacker AG.

Solvin™ 250SB is a copolymer of vinyl chloride and vinyl acetateprovided by Solvin SA, Belgium.

Ixan™ SGA1 is a copolymer of 46% vinylidene chloride, 46% vinylchloride, 3% maleic anhydride and 1% acrylonitrile provided by SolvinSA, Belgium.

Vinnol™ H11-59 is a copolymer of 89 wt % vinyl chloride and 11 wt % ofvinyl acetate provided by Wacker AG.

Vinnol™ H14/36 is a copolymer of 86 wt % vinyl chloride and 14 wt %vinyl acetate provided by Wacker AG.

Ucar™ VYHH is a high molecular weight copolymer of 86% vinyl chlorideand 14% vinyl acetate provided by Dow Chemical.

Vinnol™ H15/50 is a copolymer of 85 wt % vinyl chloride and 15 wt % ofvinyl acetate provided by Wacker AG.

Solbin™ MFK is a copolymer of 90% vinyl chloride, 7% vinyl acetate and3% acrylic acid, provided by Nissin Chemical industry Co., Japan.

Solbin™ M5 is a copolymer of 85% vinyl chloride, 14% vinyl acetate and1% of a dicarboxylic acid, provided by Nissin Chemical industry Co.,Japan.

UCAR™ VAGD is a medium molecular weight copolymer of 90% vinyl chloride,4% vinyl acetate and 6% vinylalcohol, provided by Dow Chemical.

Solbin™ AL is a copolymer of 93% vinyl chloride, 2% vinyl acetate and 5%vinylalcohol provided by Nissin Chemical industry Co., Japan.

Solbin™ A is a copolymer of 92% vinyl chloride, 3% vinyl acetate and 5%vinylalcohol provided by Nissin Chemical industry Co., Japan.

Solvin™ 561SF is a vinylchloride-vinylacetate copolymer with 6% vinylacetate, provided by Solvin SA, Belgium.

DMF is dimethylformamide.

DMA is dimethylacetamide.

THF is tetrahydrofuran.

IR-1 is a 0.15 wt % solution in MEK of the infrared dye CASRN223717-84-8 and was prepared as described below.

The synthesis of intermediate INT-5 was carried out in a cascade modewithout purification of the intermediates INT-1, INT-2, INT-3 and INT-4as described below:

Intermediate INT-1

To a solution of butyl isocyanate (1.03 eq.) in toluene (70 mL/mol) at50° C. was added 2-amino-1-methoxy propane (1.00 eq.) over a 2 hourperiod. After stirring for 30 minutes, excess toluene and reagent weredistilled off at 85° C./50 mbar and at 85° C./20 mbar respectively. Themixture was allowed to reach atmospheric pressure under nitrogen.

Intermediate INT-2

To the warm residue (INT-1) were consecutively added: acetic acid (140mL/mol), malonic acid (1.00 eq.) and acetic anhydride (2.00 eq.). Understirring the reaction mixture was gently warmed to 90° C. After stirringfor 2.5 hours at 90° C., methanol (70 mL/mol) was added and the mixturewas refluxed for 45 minutes. Subsequently, the solvents were removed at100° C./70 mbar. After cooling to 30° C., methyl t. butyl ether (MTBE)(300 mL/mol) was added. This mixture was extracted 3× with a 5% NaClsolution in water and 2× with a satured NaCl solution in water. The MTBEwas distilled off at 95° C./70 mbar. The remaining water wasazeotropically removed with toluene. The mixture was allowed to reachroom temperature under nitrogen at atmospheric pressure.

Intermediate INT-3

To the residue (INT-2) were consecutively added under a nitrogen blanketat room temperature: cyclopentanone (1.10 eq.), ammoniumacetate (0.07eq.) and methanol (150 mL/mol). After refluxing for 4.5 hours, methanolwas distilled off at 50 mbar. Remaining methanol and water wereazeotropically removed with toluene. After cooling to room temperature,toluene (0.108 kg/mol) was added. This solution was filtered on astainless steel filter covered with silica (30 g/mol). The reactor andthe filter cake were washed with toluene (4×50 mL/mol). This solution ofINT-3 was directly used in the next step

Intermediate INT-4

To the toluene solution of INT-3 at room temperature was added aceticacid (1.00 eq.). Under a nitrogen blanket, DMF-DMA (1.13 eq.) wasquickly (10 minutes) added at 10° C. After 5 minutes, n. hexane (830mL/mol) was added, followed by another portion of n. hexane (415 mL/mol)after 30 minutes. After stirring for at least 1 hour (crystallisation)INT-4 is collected by filtration. After washing with n. hexane/toluene(100 mL/mol) and n. hexane (3×125 mL/mol), the product INT-4 wasdigested with n. hexane (500 mL/mol), filtered and dried at 25° C. for24 hours.

Intermediate INT-5

To a suspension of INT-4 in ethyl acetate (320 mL/mol) under nitrogen atroom temperature was added DMF-DMA (3.49 eq.) in one portion. Themixture was heated to 65° C. and stirred at 65° C. for 25 minutes. Whilequickly cooling to 15° C., a mixture of MTBE (640 mL/mol) and n. hexane(160 mL/mol) was added. After stirring for 15 minutes, the product wasfiltered and consecutively washed with ethylacetate/MTBE 80/20 (200mL/mol), ethylacetate/n. hexane 80/20 (200 mL/mol), ethylacetate/n.hexane 50/50 (200 mL/mol) and n. hexane (200 mL/mol). The ratherunstable product (INT-5) was dried at 25° C. for 24 hours.

The synthesis of intermediate INT-7 was carried out in a cascade modewithout purification of the intermediate INT-6 as described below:

Intermediate INT-6

To a nitrogen blanketed solution of 1,8-Naphtholactam (1.00 eq.) insulfolane (250 mL/mol) at 70° C. were added potassium iodide (0.20 eq.)and dimethylaminopyridine (DMAP) (0.135 eq.).

To this mixture was added potassium hydroxide (KOH) (0.60 eq.) and2-bromo pentane (0.50 eq.).

After 1 hour at 70-75° C. another portion of KOH (0.60 eq.) and 2-bromopentane (0.50 eq.) were added, while distilling of the pentene sideproduct. This was repeated 2 times. After cooling the reaction mixturewas diluted with MTBE (1 L/mol) and washed with water. The water layerwas extracted again with MTBE. The combined extracts were washedconsecutively with a 15% NaCl solution in water, a 10% NaCl solution inwater containing 4% HCl, a 15% NaCl solution in water containing 1%NaHCO3 and a 25% NaCl solution in water. The MTBE was distilled off andthe remaining water was azeotropically removed with toluene. The crudeINT-6 (oil) was used a such.

Intermediate INT-7

To nitrogen blanketed solution of INT-6 (1.00 eq.) in THF (100 mL/mol)at room temperature was added methyl magnesiumchloride (1.28 eq.) over45 minutes (55-60° C.). After stirring for 1 hour at 55° C., thereaction mixture was added to a mixture of HCl (3.9 eq.) in icewater(3.66 kg/mol). After distillative removal of the THF, the aqueoussolution was filtered and added to a solution of KI (2.00 eq.) in water(2.1 L/mol). After crystallisation, crude INT-7 was filtered andconsecutively washed with water (2.55 L/mol) and ethyl acetate (2.55L/mol) and dried at 40° C.

Yield: 76%

IR-absorber IR-1

To a stirred suspension of INT-5 (1.00 eq.) in methyl acetate (4 L/mol)at 50° C., was added in portions INT-7 (2.10 eq.) over 5 minutes. Afterstirring for 1 hour at 55° C., 2 extra portions of INT-7 (each 0.016eq.) were added. After stirring for 2.5 hours at 55° C., the reactionmixture was cooled to room temperature. Crude IR-1 was isolated byfiltration and washed with ethyl acetate (4 L/mol).

After digestion in water (to remove salts) (4 L/mol), filtering andwashing on the filter with water (2 L/mol) and MTBE (1.5 L/mol) theproduct was dried at 40° C. Yield=92%.

Measurement Methods 1. Optical Density

The optical density was measured in reflection using aspectrodensitometer Type Macbeth TR924 using a visual filter.

2. Adhesion

The adhesion was evaluated according to the method described inISO10373-1:1998-5.3 Peel strength

The conditions used were:

-   -   Relative humidity 50% at 23° C.    -   Measurement cell 500 N    -   Speed of 300 mm/min    -   Width of 10 mm

The norm laid down in ISO 10373-1 is ≧3.5 N/cm. In this application, theadhesion is considered excellent (“OK”) if the peel strength had a valueof ≧6 N/cm, in the alternative case the adhesion is considered to beinsufficient (“NOK”).

Example 1

This example illustrates that a good image quality colour formation andadhesion can be obtained with a security document precursor containing apolymeric binder in accordance with present invention.

Preparation of PET-C foil PET1

A coating composition SUB-1 was prepared by mixing the componentsaccording to Table 1 using a dissolver.

TABLE 1 Components of SUB-1 wt % deionized water 76.66 CCE 18.45resorcinol 0.98 PAR-sol 0.57 PEA-sol 0.68 DOW-sol 1.33 Surfynsol 1.33

A 1100 μm thick polyethylene terephthalate sheet was firstlongitudinally stretched and then coated with the coating compositionSUB-1 to a wet thickness of 10 μm. After drying, the longitudinallystretched and coated polyethylene terephthalate sheet was transversallystretched to produce a 63 μm thick sheet PET1, which was transparent andglossy.

Preparation of Colourless Colour forming Layer

The coating compositions COL-1 to COL-19 were all prepared in the sameway by mixing the components according to Table 2 using a dissolver butusing the polymer POL as given by Table 3.

TABLE 2 Components of COL-1 wt % Baysilon 1.20 MEK 6.71 Polymer POL56.96 IR-1 29.20 HDP 3.08 CVL 2.85

TABLE 3 Coating composition Polymer POL COL-1 S-Lec ™ BL5 HP Z COL-2Elvacite ™ 2010 COL-3 CAB 381-2 COL-4 Vinnol ™ E15/48A COL-5 UCAR ™ VAGCCOL-6 Vinnol ™ H40/43 COL-7 Vinnol ™ H40/60 COL-8 Solvin ™ 250SB COL-9Ixan ™ SGA1 COL-10 Vinnol ™ H11-59 COL-11 Vinnol ™ H14/36 COL-12 Ucar ™VYHH COL-13 Vinnol ™ H15/50 COL-14 Solbin ™ MFK COL-15 Solbin ™ M5COL-16 UCAR ™ VAGD COL-17 Solbin ™ AL COL-18 Solbin ™ A COL-19 Solvin ™561SF

Each coating composition COL-1 to COL-19 was coated with an ElcometerBird Film Applicator (from ELCOMETER INSTRUMENTS) on the subbed PET-Csupport PET1 at a coating thickness of 100 μm and subsequently dried for2 minutes at 20° C. on the film applicator and for a further 15 minutesin an oven at 75° C. to deliver the security films SF-1 to SF-19.

Preparation of Security Document Precursors

The security films SF-1 to SF-19 were then laminated onto a 500 μmopaque PETG core from WOLFEN to deliver the security document precursorsSDP-1 to SDP-19.

The lamination was performed using an Oasys OLA6/7 plate laminator withthe settings: LPT=115° C., LP=40, Hold=210 sec, HPT=115° C., HP=40 andECT=50° C.

Evaluation and Results

After lamination, a test image containing a wedge with differentgrey-levels (ten squares of 7×9 mm) was laser marked on the securitydocument precursors SDP-1 to SDP-19 through the PET-C foil using a RofinRSM Powerline E laser (10 W) with settings 33 ampere and 44 kHz.

The adhesion, the minimum optical density D_(min) of the non-lasermarked square and the maximum optical density were determined for allthe samples. The value of ΔD is the difference between D_(max) andD_(min) is indicative for the number of grey levels that can beobtained. The higher ΔD, the more grey levels and thus the better theimage quality. A good image quality requires a ΔD of at least 0.75 and aDmin of less than 0.50, preferably less than 0.35. The results are shownby Table 4.

TABLE 4 Laser wt % wt % marked Chlorinated Vinyl Sample ethylene acetateAdhesion D_(min) D_(max) ΔD SDP-1 0 1.4 NOK 0.32 0.32 0.00 SDP-2 0 0 NOK0.22 0.22 0.00 SDP-3 0 0 NOK 0.28 0.28 0.00 SDP-4 84 0 OK 0.48 0.94 0.46SDP-5 80 20 OK 0.39 0.88 0.49 SDP-6 66 34 NOK 0.25 0.62 0.37 SDP-7 61 39NOK 0.53 0.84 0.31 SDP-8 100 0 NOK 0.25 1.18 0.93 SDP-9 92 0 OK 0.531.08 0.55 SDP-10 89 11 NOK 0.23 1.31 1.08 SDP-11 86 14 NOK 0.25 0.780.53 SDP-12 86 14 NOK 0.25 1.16 0.91 SDP-13 85 15 NOK 0.25 1.08 0.83SDP-14 89 6.5 OK 0.54 1.31 0.77 SDP-15 85 14 NOK 0.34 1.24 0.90 SDP-1690 4 OK 0.33 1.16 0.83 SDP-17 93 2 OK 0.40 1.17 0.77 SDP-18 92 3 OK 0.421.23 0.81 SDP-19 93 7 OK 0.24 1.14 0.90

From Table 4, it should be clear that only the security documentprecursors SDP-16 to SDP-19 containing a polymeric binder in accordancewith the invention exhibit good image quality and adhesion.

1.-15. (canceled)
 16. A security document precursor including, in order:a) at least one transparent biaxially stretched polyester foil; b) atleast one colourless colour forming layer containing at least aninfrared absorber, a colourless dye-precursor and a polymeric binder;and c) a polymeric support; wherein the polymeric binder is a copolymerincluding at least 90 wt % of a chlorinated ethylene and 1 wt % to 10 wt% of vinyl acetate both based on the total weight of the binder.
 17. Thesecurity document precursor according to claim 16 wherein thechlorinated ethylene includes vinyl chloride.
 18. The security documentprecursor according to claim 17 wherein the polymeric binder includes atleast 90 wt % of vinyl chloride
 19. The security document precursoraccording to claim 17 wherein the polymeric binder includes at least 4wt % of vinyl acetate.
 20. The security document precursor according toclaim 18 wherein the polymeric binder includes at least 4 wt % of vinylacetate.
 21. The security document precursor according to claim 16wherein the infrared absorber is an infrared dye.
 22. The securitydocument precursor according to claim 16 wherein the colourlessdye-precursor is a colourless leuco dye.
 23. The security documentprecursor according claim 22 further including a hydrogen donorprecursor.
 24. The security document according to claim 23 containing4,4′-Bis(tert-butoxycarbonyloxy)diphenylsulfone as hydrogen donorprecursor and crystal violet lactone as colourless leuco dye.
 25. Thesecurity document precursor according to claim 16 containing electroniccircuitry.
 26. The security document precursor according to claim 16wherein the transparent biaxially stretched polyester foil is atransparent biaxially stretched polyethylene terephthalate foil.
 27. Asecurity document obtained by laser marking the security documentprecursor according to claim
 16. 28. The security document according toclaim 27, which is selected from the group consisting of a passport, apersonal identification card, and a product identification document. 29.The security document according to claim 28 wherein the productidentification document is attached to the packaging material of theproduct or to the product itself.
 30. A method for making a securitydocument precursor by coating on a transparent biaxially stretchedpolyester foil at least one colourless colour forming layer containingat least an infrared absorber, a colourless dye-precursor, and apolymeric binder; wherein the polymeric binder is copolymer including atleast 90 wt % of a chlorinated ethylene and 1 wt % to 10 wt % of vinylacetate both based on the total weight of the binder.
 31. The methodaccording to claim 30 wherein the polymeric binder includes at least 90wt % of vinyl chloride.